DESCRIPTION: (Applicant's Abstract) Studies targeting subgroups of cocaine abusers are needed because poor treatment outcome may, in part, be the result of comorbid psychiatric disorders. One subgroup that may benefit from targeted pharmacologic treatment is cocaine abusers who have adult attention-deficit hyperactivity disorder (ADHD). The prevalence of this disorder is substantially higher in treatment-seeking cocaine abusers (11%) than in the general population (1-3%). Given the comorbidity of ADHD and cocaine abuse, pharmacotherapies aimed at treating both disorders may be particularly effective. Methylphenidate (MPH), currently one of the most effective and safe treatments for childhood and adult ADHD, is a promising candidate. Individuals may be using cocaine to self-medicate their ADHD symptoms, due to an underlying dopamine deficit. Treating the underlying psychiatric disorder (ADHD) with MPH, may result in a reduction in cocaine use, as well as a reduction in ADHD symptoms. In the human laboratory we have shown that sustained-release MPH does not produce clinically significant cardiovascular changes, even during repeated dosing of cocaine. Further, a high maintenance dose of sustained-releaser MPH, unlike a low dose of sustained-release MPH, is more likely to reduce cocaine craving during repeated cocaine administration. Within the clinic setting, we have also shown that MPH is well-tolerated, not abused, and may be an effective treatment for cocaine abuse in adults with ADHD. Taken together, these findings suggest that double-blind, placebo-controlled trial to evaluate the effectiveness of sustained-release methylphenidate (MPH) is warranted. Specific Aims: 1) To determine if sustained-release MPH is more effective than placebo in reducing cocaine and other drug use in cocaine abusers with adult ADHD. 2) To determine if sustained-release MPH is more effective than placebo in reducing ADHD symptoms in cocaine abusers with adult ADHD. 3) To determine if improvement in ADHD symptoms precedes a reduction in cocaine use.